Pump Assembly

ABSTRACT

A pump assembly, which comprises at least one housing and two gear wheels as transfer means as well as a drive shaft. The housing comprises at least one base and one cover element, which can be connected together in order to constitute a pressure chamber. Each of the two gear wheels has a toothing on an outer circumferential surface and mesh with one another via the toothing in order to transfer a fluid. The gear wheels are arranged in an axial direction between the base and the cover element in the pressure chamber. The drive shaft extends into the housing in the axial direction via an opening in the cover element. The first gear wheel is arranged on a first bearing bush, wherein the first bearing bush is mounted only in the base. The first gear wheel is connected to the drive shaft via a formfitting connection in a circumferential direction.

The invention relates to a pump assembly. The pump assembly is envisaged for the purpose of conveying a fluid. The pump assembly comprises a housing, transfer means in the housing for conveying a fluid from a fluid inlet to a fluid outlet and a drive shaft for driving the transfer means. The fluid inlet and the fluid outlet are arranged on the housing. At least one of the transfer means is driven by the drive shaft, which extends from outside the housing into the housing. Two gear wheels meshing with one another are envisaged here as transfer means. Each gear wheel has a toothing on the circumferential surface, wherein the gear wheels are connected to one another via the toothing. The drive shaft is assigned to an electrical drive, for example, which is arranged outside the housing of the pump assembly.

The gear wheels have axes of rotation, which are oriented in particular in an axial direction. The gear wheels are arranged next to one another in a radial direction and overlapping in the axial direction, wherein the axes of rotation are arranged parallel to one another.

The drive shaft likewise has an axis of rotation, which is arranged in particular parallel to the axes of rotation of the gear wheels and preferably coaxially with the axis of rotation of a gear wheel.

In a suchlike pump assembly the transfer means can be arranged on shafts, and the shafts can be mounted on bearing locations to either side of the transfer means in the housing. Furthermore, a drive shaft can be connected directly to the transfer means, and the transfer means can be mounted above the drive shaft on bearing locations. The expression mounted is used here to denote, in particular, that forces acting in a radial direction (additionally in an axial direction, if appropriate) can be transferred at least in a radial direction (also in the axial direction, if appropriate) via the transfer means onto the shaft or onto the bearing of the shaft in the housing (that is to say, for example, onto the base and the cover element). Supporting the shaft on both sides of the transfer means requires accurate adjustment of the positional tolerances of the bearing locations on the housing, however. In particular, uneven loadings of the bearing locations and bending loadings of the shafts can occur.

With this in mind, the object of the present invention is at least partially to address the problems described with regard to the prior art. In particular, a pump assembly of the simplest and lightest possible embodiment is proposed, the intention being to reduce or even prevent uneven loading of the bearing locations.

To accomplish said object, a pump assembly according to the characterizing features of patent claim 1 is proposed. Advantageous further developments are the subject-matter of the dependent patent claims. The characterizing features listed individually in the patent claims can be combined with one another in a technically expedient manner and can be supplemented by explanatory facts from the description and by details from the figures, wherein further variant embodiments of the invention are proposed.

This is assisted by a pump assembly, wherein the pump assembly comprises at least the following components:

one housing having at least one base and one cover element, which can be connected together in order to constitute a pressure chamber;

(at least) two gear wheels (as transfer means), wherein the gear wheels each have a toothing on an outer circumferential surface and mesh with one another via the toothing in order to transfer a fluid; wherein the gear wheels are arranged in an axial direction between the base and the cover element in the pressure chamber; and

a drive shaft, which extends into the housing in the axial direction through an opening in the cover element.

At least a first gear wheel of the two gear wheels is capable of being driven as an input gear wheel by the drive shaft. At least the first gear wheel is embodied as a ring gear, wherein the first gear wheel is arranged on a first bearing bush. The first bearing bush is mounted only in the base. The first gear wheel is connected to the drive shaft via a formfitting connection in a circumferential direction.

In particular, the second gear wheel is also embodied as a ring gear, wherein the second gear wheel can be arranged on a second bearing bush. The second bearing bush can be mounted (only or alternatively) in the base or the cover element.

Two gear wheels meshing with one another are envisaged here as transfer means. Each gear wheel has a toothing on the outer circumferential surface, wherein the gear wheels are connected to one another via the toothing. Each of the gear wheels has an axis of rotation, which is oriented in particular in an axial direction. The gear wheels are arranged next to one another in a radial direction and overlapping one another in the axial direction, wherein the axes of rotation are arranged parallel to one another.

The drive shaft likewise has an axis of rotation, which in particular is arranged parallel to the axes of rotation of the gear wheels and preferably coaxially with the axis of rotation of a gear wheel.

The housing is constituted by at least one base and one cover element. These are arranged one after the other in the axial direction, wherein the gear wheels are positioned between them. The base and the cover element enclose the gear wheels externally in a radial direction and as such constitute the pressure chamber. The pressure chamber is connected to a fluid inlet and a fluid outlet, so that a fluid can be supplied to the fluid outlet via the fluid inlet and the pressure chamber.

In particular, the bearing bushes are embodied as so-called plain bearings or friction bearings. In the plain bearing/friction bearing, both of the parts that move relative to one another (in this case, the gear wheel and the bearing bush or the bearing bush and the housing, that is to say the base and the cover element) are in direct contact. They slide on one another against the resistance caused by sliding friction. This can be kept at a low level by the choice of a low-friction material combination, by lubrication or by the creation of a lubricating film (full fluid film lubrication), which separates the two contact surfaces from one another. It is also possible to envisage roller bearings, however, wherein one roller bearing is arranged between the housing and the bearing bush or between the bearing bush and the gear wheel.

In particular, the fluid supplied by the pump serves as a lubricant for the bearing. In this case, special fluid passageways can be envisaged in the base and/or the cover element, through which a part of the fluid supplied by the pump is guided to the bearing location.

It is proposed here that at least the first gear wheel, and in particular each gear wheel which acts as a transfer means, is mounted above the bearing bush only on one side of the gear wheel (or unilaterally) in the housing (that is to say either in the base or in the cover element, and in the case of the first gear wheel in the base). The bearing bush envisaged for supporting each gear wheel extends, starting from the gear wheel, only to the base or to the cover element. As a result, the bearing bush is mounted or secured only on one side of the gear wheel in the housing, and thus has only one (individual) bearing location. Forces acting in the radial direction are thus transferred onto the housing from the gear wheel onto the bearing bush (via the bearing location between the gear wheel and the bearing bush) and from the bearing bush via the bearing location that is present only on one side of the gear wheel (between the bearing bush and the housing).

In particular, both component parts of the group that is made up of the first bearing bush and the second bearing bush are mounted or secured only in the base. In particular, both bearing bushes extend, starting from the respective gear wheel, in the direction of the same part of the housing, that is to say also in the same axial direction.

This arrangement is particularly advantageous, because in this way appropriate tolerancing of the position must be undertaken only on one of the parts of the housing, that is to say on the base.

It is proposed, in particular, that a sliding contact bearing is envisaged between the (each) bearing bush and the (respective) gear wheel embodied as a ring gear. The bearing bush is preferably arranged in a fixed or non-detachable manner in the housing (that is to say in the base or in the cover element), so that in particular a new bending loading of the bearing bush can be reduced or a defined transfer of force from the bearing bush onto the housing can take place between the bearing bush and the housing via the bearing location.

In particular, an intermediate element is arranged in the axial direction between the base and the cover element, wherein the intermediate element encloses the gear wheels externally in a radial direction and together with the base and the cover element constitutes the pressure chamber. The intermediate element is in particular a disc element, which is toleranced with regard to a width of the gear wheels and thus defines a length of the pressure chamber in the axial direction.

In particular, at least the base and the cover element (additionally the intermediate element, if appropriate) are aligned with one another and are connected to one another via connecting elements. In particular, at least one of the connecting elements extends in the axial direction through the intermediate element and connects the base and the cover element.

It is proposed here that at least the first gear wheel is capable of being driven as an input gear wheel via a drive shaft, wherein the drive shaft is connected (directly) to the input gear wheel through an opening in the cover element.

It is possible to drive each of the gear wheels respectively via a drive shaft.

In particular, via the drive shaft, no force acting in the radial direction, starting from the gear wheels, is transferred via the drive shaft onto the housing. In particular, the drive shaft thus transfers only a driving torque acting in the circumferential direction onto the input gear wheel.

In particular, the drive shaft is arranged with respect to the first gear wheel and the first bearing bush in a radial direction with a free clearance. The expression free clearance is used in this context to denote that a certain displacement of the drive shaft with respect to the first gear wheel in the radial direction is possible, but without a force being transferred by the drive shaft onto the first gear wheel or vice versa in the radial direction. In particular, a free clearance of at least 0.2 mm [millimeters], and preferably of at least 0.5 mm, is envisaged so that, in the event of a concentric arrangement of the drive shaft and the first gear wheel, a displacement of at least 0.2 mm (or of at least 0.5 mm) in the radial direction is possible in the manner described above.

In particular, the drive shaft is arranged mounted exclusively outside the housing with respect to a force acting in a radial direction.

The drive shaft is preferably a component part of an electrical drive or of a gearbox, for example, wherein the drive shaft is mounted on at least two bearing locations arranged at a distance from one another in the axial direction (although always outside the housing).

The formfitting connection by an inner circumferential surface of the first gear wheel and an outer circumferential surface of the drive shaft (acting in the circumferential direction) is preferably constituted, for example, by an inner toothing of the first gear wheel and an outer toothing of the drive shaft.

In particular, the drive shaft and the first gear wheel or the drive shaft and the first bearing bush constitute an abutment against displacement in the axial directions. Positioning of the drive shaft and the first gear wheel in the axial direction is possible by means of the abutment. In particular, a free clearance between the drive shaft and the first gear wheel or between the drive shaft and the first bearing bush is envisaged in the operation of the pump assembly, so that no axial forces can be transferred.

In particular, the drive shaft has a reduction on its end face, so that the drive shaft, as it is introduced into the housing, for example, can be guided with respect to the radial direction by the first bearing bush. In particular, the reduction on the end face serves only to ensure a free clearance between the drive shaft and the first bearing bush in the operation of the pump assembly. As a result, it is possible to ensure that no forces acting in the radial direction are transferred.

In particular, the first bearing bush is connected to the base via a press fit. The second bearing bush is preferably connected (alternatively) to the base or the cover element via a press fit. The expression press fit is used in this context to denote that, before joining together the bearing bush and the housing, an external diameter of the bearing bush is (slightly) larger than an internal diameter of the locating bore (in the housing) for the bearing bush.

In particular, the first bearing bush is connected in an integrally bonded manner to the base and is formed integrally with the base The second bearing bush is preferably connected in an integrally bonded manner to and integrally formed with the base or the cover element (e.g. executed as a single-part or multi-part green compact and then sintered together). The expression integrally bonded manner is used to denote all connections in which the connection partners are held together by atomic or molecular forces. At the same time, they are non-separable connections, which can be parted only by destruction of the connection means.

In particular, at least the base and the cover element are embodied at least partially as sintered parts. In particular, at least the first bearing bush is embodied as a sintered part. Preferably, both bearing bushes are embodied at least partially as sintered parts. Most preferably, at least one of the following component parts and, if appropriate, several or all of the following component parts are executed as a sintered part: the base, the cover element, the intermediate element, the bearing bushes, the gear wheels, the connecting elements.

A sintered part is a component part (green compact) pressed from a material in powder form, which has subsequently been subjected to a sintering process. In particular, at least one, and preferably all of: the base, the cover element, the intermediate element, the bearing bushes, the gear wheels, the connecting elements, are produced from a metallic powder by pressing and sintering. In particular, bearing bushes and the part of the housing receiving the bearing bushes are produced as separate green compacts (preferably from different materials), which are joined to one another as green compacts (preferably including the creation of a press fit) and are then sintered together.

It should be noted, for the avoidance of any doubt, that the numerals (“first”, “second”, . . . ) that are used here serve primarily (only) to distinguish between a number of similar objects or sizes, that is to say in particular they do not necessarily define any dependence and/or sequence of these objects or sizes in relation to one another. Should a dependence and/or a sequence be required, this is indicated explicitly here or it will become apparent to a person skilled in the art from a study of the embodiment described in concrete terms.

The invention and the technical environment are explained in more detail below on the basis of the figures. It should be pointed out at this point that the invention is not intended to be restricted by the illustrative embodiments shown here. In particular, it is also possible, unless explicitly stated to the contrary, to extract partial aspects of the facts presented in the figures and to combine them with other component parts and findings from the present description and/or figures. In particular, it must be pointed out that the figures and, in particular, the represented size ratios are only schematic. Identical reference designations designate identical objects, so that explanations from other figures can be used in a complementary manner, if appropriate. In the figures:

FIG. 1: depicts a first pump assembly in a perspective view and in an exploded view;

FIG. 2: depicts the pump assembly according to FIG. 1 in a side view in cross section;

FIG. 3: depicts a further pump assembly in a side view in cross section;

FIG. 4: depicts the pump assembly according to FIG. 3 in a further side view;

FIG. 5: depicts a pump assembly in a perspective view and in an exploded view;

FIG. 6: depicts a detail of the pump assembly according to FIG. 5 in a side view;

FIG. 7: depicts a further detail of the pump assembly according to FIG. 5 in a side view; and

FIG. 8: depicts the detail according to FIG. 7 in a further side view.

FIG. 1 depicts a first, known pump assembly 1 in a perspective view and in an exploded view. FIG. 2 depicts the pump assembly 1 according to FIG. 1 in a side view in cross section. FIGS. 1 and 2 are described jointly below.

The pump assembly 1 comprises a housing 2 and transfer means in the housing 2 for conveying a fluid from a fluid inlet 20 to a fluid outlet 21. The fluid inlet 20 and the fluid outlet 21 are arranged on or in the housing 2. The housing 2 comprises a base 3 and a cover element 4 and an intermediate element 12, which can be connected together by connecting elements 24 in order to constitute a pressure chamber 5. The transfer means are arranged in the pressure chamber 5 in an axial direction 9 between the base 3 and the cover element 4. The intermediate element 12 encloses the gear wheels 6, 7 externally in a radial direction 13. The intermediate element 12 is a disc element, which is toleranced with regard to a width of the gear wheels 6, 7 and thus defines a length 17 of the pressure chamber 5 in the axial direction 9. One of the transfer means is driven via a drive shaft 15, which extends from outside the housing 2 into the housing 2. Two gear wheels 6, 7 meshing with one another are envisaged here as transfer means. Each gear wheel 6, 7 has a toothing 8 on the outer circumferential surface, wherein the gear wheels 6, 7 are connected to one another via the toothing 8 in order to transfer a fluid.

The gear wheels 6, 7 have axes of rotation 22, which are oriented in an axial direction 9. The gear wheels 6, 7 are arranged next to one another in a radial direction 13 and overlapping in the axial direction 9, wherein the axes of rotation 22 are arranged parallel to one another.

The transfer means are arranged on shafts 15, 23, and the shafts 15, 23 are mounted on bearing locations 19 (e.g. via a sliding contact bearing 18) to either side of the transfer means in the housing 2, that is to say in this case in the base 3 and in the cover element 4. Furthermore, a drive shaft 15 is connected directly to the transfer means, and the transfer means are mounted above the drive shaft 15 on bearing locations 19. The expression mounted is used in this context to denote that forces acting in a radial direction 13 (if appropriate, additionally in an axial direction 9) are transferred at least in a radial direction 13 (if appropriate, also in the axial direction 9) by the transfer means onto the shaft 15, 23 or onto the bearing location 19 of the shaft 15, 23 in the housing 2. However, supporting the shaft 15, 23 on both sides of the transfer means requires accurate adjustment of the positional tolerances of the bearing locations 19 on the housing 2. Uneven loadings of the bearing locations 19 and bending loadings of the shafts 15, 23 can occur here.

FIG. 3 depicts a further pump assembly 1 in a side view in cross section. FIG. 4 depicts the pump assembly 1 according to FIG. 3 in a further side view in cross section. FIGS. 3 and 4 are described jointly below. Reference is made to the embodiments in FIGS. 1 and 2.

The pump assembly 1 comprises a housing 2 and two gear wheels 6, 7 as transfer means. The housing 2 comprises a base 3, an intermediate element 12 and a cover element 4, which can be connected together by connecting elements 24 (as depicted in FIGS. 1 and 2) in order to constitute a pressure chamber 5. Each of the two gear wheels 6, 7 have a toothing 8 on an outer circumferential surface and mesh with one another via the toothing 8 in order to transfer a fluid. The gear wheels 6, 7 are arranged in an axial direction 9 between the base 3 and the cover element 4 in the pressure chamber 5. The first gear wheel 6 and the second gear wheel 7 are embodied respectively as a ring gear, wherein the second gear wheel 7 is arranged on a second bearing bush 11 and the first gear wheel 6 is arranged directly on the drive shaft 15. The second bearing bush 11 is arranged only in the cover element 4. The gear wheels 6, 7 have axes of rotation 22, which are oriented in an axial direction 9. The gear wheels 6, 7 are arranged next to one another in a radial direction 13 and overlapping in the axial direction 9, wherein the axes of rotation 22 are arranged parallel to one another.

The base 3, the intermediate element 12 and the cover element 4 are arranged one after the other in the axial direction 9, wherein the gear wheels 6, 7 are positioned between them. The intermediate element 12 encloses the gear wheels 6, 7 externally in a radial direction 13 and, as such, constitutes the pressure chamber 5 together with the other parts of the housing 2. The intermediate element 12 is a disc element, which is toleranced with regard to a width of the gear wheels 6, 7 and thus defines a length 17 of the pressure chamber 5 in the axial direction 9.

The second bearing bush 11 is embodied as a so-called sliding contact bearing 18. Both of the parts that move relative to one another (in this case, the second gear wheel 7 and the second bearing bush 11) are in direct contact in the sliding contact bearing 18. They slide on one another against the resistance caused by sliding friction and constitute the bearing location 19 for the second gear wheel 7.

The second gear wheel 7 is thus mounted only on one side of the second gear wheel 7 in the housing 2, in this case in the cover element 4, via a bearing location 19. The second bearing bush 11 envisaged for supporting the second gear wheel 7 extends, starting from the second gear wheel 7, only to the cover element 4. The second bearing bush 11 is thus mounted or secured only on one side of the second gear wheels 7 in the housing 2, and it thus has only one bearing location 19. Forces acting in the radial direction 13 are thus transferred to the housing 2 from the second gear wheel 7 to the second bearing bush 11 and from the second bearing bush 11 via the bearing location 19 that is present only on one side of the second gear wheel 7.

The first gear wheel 6 is arranged in this case directly on the drive shaft 15 as an input gear wheel 14. The drive shaft 15 transfers a driving torque acting in the circumferential direction 25 (see the arrow in FIG. 4) onto the input gear wheel 14. The first gear wheel 6 is not mounted in the housing 2. The drive shaft 15 extends into the housing 2 in the axial direction 9 via the opening 16. The drive shaft 15 is mounted exclusively outside the housing 2 in an electrical drive 31. Two bearing locations 19 are arranged there at a distance from one another in the axial direction 9. Forces acting in the radial direction 13 (see the arrows in FIG. 4) are led away via the drive shaft 15 into the electrical drive 31, for example starting from the first gear wheel 6.

FIG. 5 depicts a pump assembly 1 in a perspective view and in an exploded view (in this case without a drive shaft 15). The embodiments in FIG. 1 and FIG. 3 can be used in a complementary manner.

The pump assembly 1 comprises one housing 2 and two gear wheels 6, 7 as transfer means. The housing 2 comprises a base 3, an intermediate element 12 and a cover element 4, which can be connected together by connecting elements 24 (as depicted in FIGS. 1 and 2) in order to constitute a pressure chamber 5.

Each of the two gear wheels 6, 7 has a toothing 8 on an outer circumferential surface and mesh with one another via the toothings 8 in order to transfer a fluid. The gear wheels 6, 7 are arranged in the pressure chamber 5 in an axial direction 9 between the base 3 and the cover element 4. The first gear wheel 6 and the second gear wheel 7 are embodied respectively as a ring gear, wherein the first gear wheel 6 is arranged on a first bearing bush 10 and the second gear wheel 7 is arranged on a second bearing bush 11. The first bearing bush 10 and the second bearing bush 11 are arranged respectively only in the base 3. The gear wheels 6, 7 have axes of rotation 22, which are oriented in an axial direction 9. The gear wheels 6, 7 are arranged next to one another in a radial direction 13 and overlapping in the axial direction 9, wherein the axes of rotation 22 are arranged parallel to one another.

The base 3, the intermediate element 12 and the cover element 4 are arranged one after the other in the axial direction 9, wherein the gear wheels 6, 7 are positioned between them. The intermediate element 12 encloses the gear wheels 6, 7 externally in a radial direction 13 and, as such, constitutes the pressure chamber 5 together with the other parts of the housing 2. The intermediate element 12 is a disc element, which is toleranced with regard to a width of the gear wheels 6, 7 and, as such, defines a length 17 of the pressure chamber 5 in the axial direction 9. The pressure chamber 5 is connected to a fluid inlet 20 and a fluid outlet 21, so that a fluid can be supplied to the fluid outlet 21 via the fluid inlet 20 and the pressure chamber 5.

The bearing bushes 10, 11 are embodied as a so-called sliding contact bearing 18. Both of the parts that move relative to one another (in this case the gear wheel 6, 7 and the bearing bush 10, 11) are in direct contact in the sliding contact bearing 18. They slide on one another against the resistance caused by sliding friction and form the bearing location 19 for the gear wheel 6, 7.

Each gear wheel 6, 7 is thus mounted only on one side of the gear wheels 6, 7 in the housing 2, in this case in the base 3, above bearing locations 19. The bearing bush 10, 11 envisaged for supporting each gear wheel 6, 7 extends, starting from the gear wheel 6, 7, only to the base 3. The bearing bush 10, 11 is thus mounted or secured in the housing 2 only on one side of the gear wheel 6, 7, and it thus has only one bearing location 19.

A sliding contact bearing 18 is envisaged between each bearing bush 10, 11 and the gear wheel 6, 7 embodied respectively as a ring gear. The bearing bushes 10, 11 are arranged securely in the housing 2 (that is to say in the base 3).

The base 3 and the cover element 4 and additionally the intermediate element 12 are oriented in relation to one another and are connected to one another by means of connecting elements 24. The connecting elements 24 extend in the axial direction 9 through the intermediate element 12 and connect the base 3 and the cover element 4.

One of the gear wheels 6, 7 is capable of being driven as an input gear wheel 14 via a drive shaft 15 (see FIG. 6), wherein the drive shaft 15 is capable of being connected to the input gear wheel 14 through an opening 16 in the cover element 4. An inner toothing 26 can be seen to be arranged on the input gear wheel 14, which interacts with the drive shaft 15 for the purpose of driving the input gear wheel 14.

FIG. 6 depicts a detail of the pump assembly 1 according to FIG. 5 in a side view. FIG. 7 depicts a further detail of the pump assembly 1 according to FIG. 5 in a side view. FIGS. 6 and 7 are described jointly below. Reference is made to the embodiments in FIG. 5.

Only the gear wheels 6, 7, the bearing bushes 10, 11 and the drive shaft 15 are represented in FIG. 6. The base 3 is represented additionally in FIG. 7. The drive shaft 15 extends into the housing 2 (see FIG. 5) in the axial direction 9 through an opening 16 in the cover element 4. The first gear wheel 6 is connected to the drive shaft 15 in a circumferential direction 25 via a formfitting connection (in this case via the inner toothing 26).

Via the drive shaft 15, no force acting in the radial direction 13, starting from the gear wheels 6, 7, is transferred via the drive shaft 15 onto the housing 2. The drive shaft 15 thus transfers only one driving torque acting in the circumferential direction 25 onto the input gear wheel 14.

The formfitting connection acting in the circumferential direction 25 is constituted by an inner circumferential surface 28 of the first gear wheel 6 and an outer circumferential surface 29 of the drive shaft 15, in this case via the inner toothing 26 (see FIG. 5) of the first gear wheel 6 and an outer toothing of the drive shaft 15.

The drive shaft 15 and the first bearing bush 10 form an abutment 30 against displacement in the axial directions 9. Positioning of the drive shaft 15 and the first gear wheel 6 in the axial direction 9 is possible via the abutment 30. A free clearance in the axial direction 9 between the drive shaft 15 and the first gear wheel 6 and between the drive shaft 15 and the first bearing bush 10 is envisaged in the operation of the pump assembly 1.

The drive shaft 15 also has a reduction 32 on its end face, so that the drive shaft 15, for example as it is introduced into the housing 2, is guided via the first bearing bush 10 with respect to the radial direction 13.

The drive shaft 15 is arranged with respect to the first gear wheel 6 and the first bearing bush 10 with a free clearance 27 in a radial direction 13. The expression free clearance 27 denotes that a certain displacement of the drive shaft 15 with respect to the first gear wheel 6 (and with respect to the first bearing bush 10) is possible in the radial direction 13, without a force being transferred from the drive shaft 15 onto the first gear wheel 6 or vice versa in the radial direction 13. The free clearance 27 between the first gear wheel 6 and the drive shaft 15 is equivalent to one half of the difference in the diameter of the first gear wheel 6 and the drive shaft 15 in the region of the formfitting connection between the first gear wheel 6 and the drive shaft 15 in the circumferential direction 25. This formfitting connection is formed by the inner toothing 26 on the inner circumferential surface 28 of the first gear wheel 6 and the outer toothing on the outer circumferential surface 29 of the drive shaft 15. Thus, if a free clearance of 0.2 mm is envisaged, a displacement of 0.2 mm in the radial direction 13 in the manner described above is possible for a concentric arrangement of the drive shaft 15 and the first gear wheel 6. The free clearance 27 in this case is (only) so large that the formfitting connection in the circumferential direction 25 between the first gear wheel 6 and the drive shaft 15 is met in any case or at any event for a displacement of the drive shaft 15 with respect to the first gear wheel 6 in the radial direction 13).

FIG. 8 depicts the detail according to FIG. 7 in a further side view. Reference is made to the embodiments in FIG. 7. The drive shaft 15 is arranged mounted exclusively outside the housing 2 with respect to a force acting in a radial direction 13 (see the arrows in FIG. 8). The drive shaft 15 is thus a component part of an electrical drive 31, wherein the drive shaft 15 is mounted on two bearing locations 19 that are arranged separately from one another in the axial direction 9 (although always outside the housing 2). No force acting in the radial direction 13, starting from the gear wheels 6, 7, is thus transferred by the drive shaft 15 via the drive shaft 15 onto the housing 2. The drive shaft 15 transmits only a driving torque acting in the circumferential direction 25 onto the input gear wheel 14.

LIST OF REFERENCE DESIGNATIONS

-   1 pump assembly -   2 housing -   3 base -   4 cover element -   5 pressure chamber -   6 first gear wheel -   7 second gear wheel -   8 toothing -   9 axial direction -   10 first bearing bush -   11 second bearing bush -   12 intermediate element -   13 radial direction -   14 input gear wheel -   15 drive shaft -   16 opening -   17 length -   18 sliding contact bearing -   19 bearing location -   20 fluid inlet -   21 fluid outlet -   22 axis of rotation -   23 shaft -   24 connecting element -   25 circumferential direction -   26 inner toothing -   27 free clearance -   28 inner circumferential surface -   29 outer circumferential surface -   30 abutment -   31 electrical drive -   32 reduction 

1. A pump assembly, comprising one housing having at least one base and one cover element, which can be connected together in order to constitute a pressure chamber; two gear wheels, which respectively have a toothing on an outer circumferential surface and mesh with one another via the toothing in order to transfer a fluid; wherein the gear wheels are arranged in an axial direction between the base and the cover element in the pressure chamber; and a drive shaft, which extends into the housing in the axial direction through an opening in the cover element; wherein at least a first gear wheel is capable of being driven as an input gear wheel by the drive shaft; wherein at least the first gear wheel is embodied as a ring gear, wherein the first gear wheel is arranged on a first bearing bush, wherein the first bearing bush is mounted only in the base; wherein the first gear wheel is connected to the drive shaft via a formfitting connection in a circumferential direction.
 2. The pump assembly as claimed in claim 1, wherein the drive shaft is arranged in a radial direction with a free clearance with respect to the first gear wheel and the first bearing bush.
 3. The pump assembly as claimed in claim 1, wherein the drive shaft is arranged mounted exclusively outside the housing with respect to a force acting in a radial direction.
 4. The pump assembly as claimed in claim 1, wherein the formfitting connection is constituted by an inner circumferential surface of the first gear wheel and an outer circumferential surface of the drive shaft.
 5. The pump assembly as claimed in claim 1, wherein the drive shaft and the first gear wheel or the drive shaft and the first bearing bush constitute an abutment against displacement in the axial directions.
 6. The pump assembly as claimed in claim 1, wherein the first bearing bush is connected to the base via a press fit.
 7. The pump assembly as claimed in claim 1, wherein the first bearing bush is connected in an integrally bonded manner to and formed integrally with the base.
 8. The pump assembly as claimed in claim 1, wherein at least the base and the cover element are embodied at least partially as sintered parts.
 9. The pump assembly as claimed in claim 1, wherein at least the first bearing bush is embodied as a sintered part.
 10. The pump assembly as claimed in claim 1, wherein the second gear wheel is also embodied as a ring gear, wherein the second gear wheel is arranged on a second bearing bush, wherein the second bearing bush is mounted only in one or other of the base and the cover element. 